Process of treating coal



atenteci Apr. iii, lg

PROCESS OF TREATING COAL RobertE. Burk, Cleveland Heights, and Einar Kropp.

Cleveland, Ohio, assignors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application May 18, 1940, Serial No. 336,012

Claims.

This invention relates to the treating and handling of coal, and more particularly the preparation and handling of coal in slurries, pumpable in water; and it is among the objects of the invention to condition the coal in particularly effective manner for handling and utilization. Other objects and advantages will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinaf r'fully described, and particularly pointed out n the claims, the following description setting forth in detail certain illustrative .embodiments of the invention, these being indicative .however, of but a few of the various ways in which the principle of the invention may be employed.

In preparing coal slurries, we have found that there is substantially no lower limit to particle size insofar as pumping line transportation of the slurry is concerned, nor to the handling at point of disposal; but the presence of excessive fines will increase the settling time and filtration time at the delivery end of the line. And, we have found that operating with particles small enough to pump, but with a minimum of fines decreases grinding time, decreases settling time, increases filter capacities, and in certain instances avoids drying at the receiving end, and for all these considerations it is found that grinding such that eighty-five per cent of the particles pass a two hundred mesh screen and ninety-five per cent pass a one hundred mesh screen, gives particularly advantageous results with respect to the various factors concerned in preparaing and handling and using.

The coal, unless already of a size suitable to go into a wet grinding mill, is crushed. It is then ground in the presence of water by a suitable means, as for instance desirably wet ball mills of continuous type or the like, and is then passed through successive zones of classifying. We have found that if the coal be ground and the customary wet ways first be employed to separate out over-size particles, there is considerable difficulty because of the low density of the coal which for this reason requires very large over-size capacity in such means.

A desirable separation however may be carried out by treatment with air bubbling under suitable physical and chemical conditions for frothing separation. Thus, by treating the wet slurry in the presence of air bubbling with a wetting and frothing agent, such as cresylic acid, tannic acid, oxalic acid, aromatic sulfonic acids, hydrocarbon sulfonates or sulfates, pine oil, soaps, etc., the fines taken off from the first zone or flotation cell are thereby conditioned to a size to go into the- I land (McGraw-Hill Book C0,, Inc., New York,

1937), pages 308 and 310; the coal ground in a wet mill to a pulp being supplied to the flotation zone, through the porous bottom of which air is,

bubbled, and the desired fine particles of coal are taken off in the foam at the top, while the discharge of the remaining eilluent is passed to one or more succession cells to effect further recovery of fine solid particles escaping the first cell, and over-size material may be returned to the ball mill. In some instances it is desirable to grind and carry out the froth separation in the presence of more water than is to be handled in the slurry through the pipe line, and in such case the fine components as coming from the first frothing zone may be passed through a means for eliminating excess water, such for instance as a thickener such as used with certain ore pulps, etc. If in the bubble classifying zones we employ as wetting and frothing agent a substance of acid type, as for example cresylic acid, then after the classification and ash separating operations this may be neutralized, as for instance by potassium hydroxide, ammonium hydroxide, ethanol amine, etc., and the compound so formed very conveniently next provides a particularly effective dispersing agent to maintain the coal particles in suspension during the transit through the pipe line. While the suitably fine material is thus taken off for transit, the over-size particles are at the sametime separately taken 'OE and recycled to the wet grinding zone. If desired, other methods of classifying not embodying air bubbling may be employed.

Where coal contains undesired amounts of min eral matter and ash-producing material this can be eliminated by passing the classifyer overthrow through a further cell or cells where, as by the choice of suitable agents, the coal particles may be selectively wetted and also carried by the air bubbles, while the mineral particles will be wetted by the water and settle out at the discharge end of the classifying zones. The slurry may then be thickened to pumping concentration and the clean over-size returned for further grinding.

In some instances it is desirable also to incorporate in the slurry before it goes into the pipe line. an addition agent for instance to restrain corrosion or to restrain oxidation, e. g., phosylene" diamine, quinoline, mercaptobenzothiazole and its derivatives, etc.

The thus prepared coal suspension is pumped through the pipe line of any desired length from point of preparation to point of usage, and at the latter point the slurry is discharged-into a settling space which may advantageously be large enough to provide a desired amount of storage thus in water and in protection from the atmosphere. equipped with conveyor means, the accumulation of coal particles at the bottom may be removed in relatively concentrated slurry without requirement of a thickener or specific means for eliminating the excess water. Then, the material may go to a continuous type filter, for example, or to a centrifuge, and to a drier of rotary or other desired form. In the drying, an inert atmosphere, such as that provided by products of combustion, should be present. And, by drawing oil to a cyclone separator, suspended dust particles may be separated from the gas, so much of the latter as desired may be re-cycled to the drier, and the recovered dust particles may be turned with the discharge particles from the drier to the bunkers, burners or other equipment which is to operate on the coal. Where it is unnecessary to dry the filtered coal, it may be by-passed in whole or in part direct from the filter to the bunkers or burners or other point of disposal as preferred. It the particle size is approximately that indicated as preferred, the drying step may generally be dispensed with. Relatively coarse coal, as'10 to 20 mesh may also be pumped on occasion with only centrifuging and further grinding at the end of the system.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

We therefore particularly point out and distinctly claim as our invention:

1. A process of treating coal, which comprises grinding coal in the presence of water to a fine ness of eighty-five per cent'two hundred mesh and ninety-five per cent one hundred mesh, subiecting the product in at least one zone to treatment with bubbled air and an acid frothing agent, returning over-sized particles to the wet grinding zone, taking oi! the fine particles from the frothing treatment, eliminating excess of water from such particles, neutralizing the acid frothing agent and changing same to a dispersing agent, incorporating in the slurry an agent lessening its oxygenizing tendencies, pumping And, by having the bottom.

the resultant slurry through a pipe line to point or use, running the slurry into a storage and settling basin, drawing on the thicker coal slurry iron: the bottom, filtering, and drying the particles in an inert atmosphere.

2. A process or treating coal, which comprises grinding coal in the presence or water to a fineness of eight-five per cent two hundred mesh and ninety-five per cent one hundred mesh, subjecting the product in at least one zone to treatment with bubbled air and an acid frothing agent, returning over-sized particles to the wet grinding zone, taking 011 the fine particles from the irothing treatment, eliminating excess of water from such particles, neutralizing the acid frothing agent and changing same to a dispersing agent, pumping the resultant slurry through a pipe line to point of use, and running the slurry into a storage and settling basin.

3. A process of treating coal, whichcomprises grinding coal in the presence 01' water to a fineness of eight-five per cent two hundred mesh and ninety-five per cent one hundred mesh, subjecting the product in a preliminary zone to bubbled air and an acid frothing agent, retuming over-sized particles to the wet grinding zone, taking off the fine particles from the preliminary zone, eliminating excess of water from such particles, neutralizing the acid frothing agent and changing same to a dispersing agent, pumping the resultant slurry through a pipe line to point of use, running the slurry into a storage and settling basin, drawing on the thicker coal slurry from the bottom, filtering, and drying the particles in an inert atmosphere.

4. A process of treating coal, which comprises grinding coal in the presence of water to a fineness of eighty-five per -cent two hundred mesh and ninety-five per cent one hundred mesh, subjecting the product in a preliminary zone to bubbled air and an acid frothing agent, returning over-sized particles to the wet grinding zone, taking ofi the fine particles from the preliminary zone, neutralizing the acid irothing agent and changing same to a dispersing agent, pumping the resultant slurry through a pipe line to point of use, running the slurry into a storage and settling basin, drawing oil. the thicker coal slurry from the bottom, filtering, and drying the particles in an inert atmosphere. 5. A process of treating coal, which comprises grinding coal in the presence of water to a fineness of eighty-five per cent two hundred mesh and ninety-five per cent one hundred mesh, subjecting the product in a preliminary zone to bubbled air and an acid frothing agent, retuming over-sized particles to the wet grinding zone, taking oiI the fine particles from'the preliminary zone, neutralizing the acid irothing agent and changing same to a dispersing agent, incorporating in the slurry an agent lessening its oxygenizing tendencies, pumping the resultant slurry through a pipe line to point of use, filtering, and drying the particles in an inert atmosphere.

ROBERT E. BURK. EINAR KROPP. 

